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A state variable filter is constructed with two integrator amplifier and a summer. The integrators are low bass filters. The output of both is mixed back to the input. This will give three resonses. A High pass, band pass and low pass response.
Figure 1: State variable filter topology
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Figure 2: Simulation of a state variable filter with opamps.
integrator
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cmos svf
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Figure 3: Overdrive 250 Analysis.
state variable biquad filter
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Figure 3: State Variable biquad filter.